You can take out your sd card, or just delete the "bootmii" folder on the root of your sd card. You can keep them on your computer for later or launch the hackmii installer and it can write those files back to your sd card.

I wouldnt delete bootmii if your wii bricks this may be the only thing to save you. I dont have the answer because I havent had this problem but I would do a thorough search of the site because I am sure it is in the autoboot settings somewhere.

remove the bootmii folder from your SD, save it somewhere safe, if you installed bootmii as boot2 then do this -

If BootMii is installed as boot2, you can make BootMii autoboot to the system menu or Homebrew Channel after a specified number of seconds of inactivity by altering sd:/bootmii/bootmii.ini by adding or changing the following lines: